Permissible and Prohibited Uses of Campaign Funds: Frequently Asked Questions and Policy Overview [August 18, 2021] [open pdf - 1MB]
From the Summary: "Many frequently asked questions about permissible and prohibited uses of campaign funds are relatively straightforward. The Federal Election Campaign Act (FECA) generally permits spending campaign funds for campaign expenses; certain officeholder expenses; charitable contributions; and contributions or transfers, within specified limits, to other political committees. Conversely, FECA prohibits spending campaign funds on items that would constitute personal use, such as mortgage or tuition payments. The Federal Election Commission (FEC) relies on a standard known as the 'irrespective test' to determine permissibility of using campaign funds. If the expense would exist in the absence of the campaign, it generally is impermissible. These issues are central to frequent constituent questions for Members of Congress and staff."
CRS Report for Congress, R46878
Congressional Research Service: https://crsreports.congress.gov/